In the metallurgical field, it is known to use vibrating or mobile conveyors with the function of conveying metal material toward a temporary storage container or a melting furnace.
The metal material can be scrap iron, hot or cold sponge iron (DRI—Direct Reduction Iron), cold cast iron in bricks or briquettes, or other metal material, and can be conveyed to a containing basket in a discontinuous or batched charging process, or to the shell of the melting furnace, in a continuous charging process.
It is also known to use apparatuses that have both the function of moving, for example by means of a conveyor, the metal material to be used for charging the melting furnace, and also the function of preheating the material, exploiting the heat contained in the fumes produced by the melting process and suitably channeled inside the conveyor. This gives a reduction in the quantity of energy needed to melt the metal material during the subsequent melting steps.
Apparatuses are known for moving and preheating metal material that comprise a conveyor provided with an oblong bearing structure, substantially horizontal and which can even be several dozen meters long. A conveyor channel is mounted on the bearing structure and has lateral containing walls on which the metal material is deposited.
A vibration device is generally associated with the bearing structure, able to impart on the bearing structure a vibrational or oscillatory motion which determines the feed of the metal material in a longitudinal direction along the conveyor channel and toward the intended container.
At least a part of the bearing structure is covered at the upper part by one or more hoods that define a closed tunnel of which, in some solutions, the conveyor channel constitutes the lower part. Inside the tunnel the hot fumes exiting from the melting furnace are made to flow, to preheat the metal material present in the conveyor channel.
One disadvantage of known movement and preheating apparatuses is that they do not sufficiently exploit the great heat contained in the fumes, and are able to heat adequately only a part of the metal material, in particular the upper part, that is, the part directly hit by the stream of fumes.
Although such apparatuses, in fact, are able to introduce at a relatively high temperature, in the order of 1300-1400° C., a large quantity of fumes inside the tunnel of which the conveyor channel is part, they are able to adequately heat only a layer equal to about 20%-30% of the total height of the metal material, which is usually about 700-1200 mm.
One disadvantageous consequence of this is connected to the fact that the metal material exits from the conveyor channel at a relatively low mean temperature to allow an effective energy saving, and also with a stratified heat development, which is not uniform and not controlled, and which can therefore cause local melting and sticking of the metal material.
Another disadvantage of known apparatuses is that they are not able to adequately exploit the heat of the fumes, which exit from the preheating tunnel at a temperature that is still quite high, that is, about 1000° C., with consequent disadvantages in terms of complications of the plant and increased process costs linked to the need to cool the fumes exiting from the preheating tunnel before they are expelled into the atmosphere.
To promote the spread of the fumes over the whole height of the metal material, some solutions provide that, in the lower part of the lateral walls of the conveyor channel, suction means are disposed that suck in a part of the fumes laterally, obliging them to pass from the top downward through the metal charge. The fumes sucked in laterally then converge in a main fume discharge pipe.
One disadvantage of this type of known apparatuses is that they are voluminous and bulky, particularly in width, with a consequent high overall weight also due to the mass of cooling liquid needed to cool the walls of the tunnel.
In the state of the art, document EP-A1-420.776 is known, which describes a device for loading scrap for a furnace, having a support plane inclined from the top downward in the direction of the roof of the furnace.
In this solution, the scrap is moved toward the furnace by means of a vibration applied to the support plane which, together with gravity, causes the scrap to descend and enter through an aperture made in the upper roof of the furnace.
After passing through the scrap and giving up to it a part of their heat, the hot fumes exiting from the furnace are sucked in through suction means disposed laterally with respect to the support plane.
Documents EP-A1-2.546.593, CN-A-201662331 and WO-A1-2011091685 illustrate other systems for loading scrap with a horizontal or inclined support plane.
One purpose of the present invention is to obtain an apparatus for moving metal material, for example intended to be subsequently melted in a melting furnace, and for preheating the material, which is able to efficiently exploit the heat of the fumes produced by the melting process in the melting furnace and which is able to take from the fumes a high quantity of heat in order to heat the metal material to a higher temperature than that which can be reached with known apparatuses.
A connected purpose is to improve the distribution of the hot fumes on the entire mass of the metal material present in the conveyor channel.
Another purpose of the present invention is to obtain an apparatus to move and preheat metal material intended to be melted in a melting furnace which has reduced overall weight and bulk compared to known apparatuses.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.